Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $249.67   10.152%   $275.0165   $275.02   $275.00   $275.00  
  Purchase #2 $187.64   5.517%   $197.9921   $197.99   $198.00   $198.00  
  Purchase #3 $158.34   3.832%   $164.4076   $164.41   $164.40   $164.40  
  Purchase #4 $248.75   4.714%   $260.4761   $260.48   $260.50   $260.50  
  Purchase #5 $131.86   11.590%   $147.1426   $147.14   $147.15   $147.10  
  Purchase #6 $234.26   10.147%   $258.0304   $258.03   $258.05   $258.00  
  Purchase #7 $141.29   4.447%   $147.5732   $147.57   $147.55   $147.60  
  7 purchase totals = $1,351.81       $1,450.6385   $1,450.64   $1,450.65   $1,450.60